Filter cartridges are widely used in the nuclear industry to filter streams containing radioactive materials. As these cartridges become exhausted and clogged they are removed and stored for later disposal. At the present time hundreds of thousands of these filter cartridges are awaiting a safe and economical method of disposal.
Disposal by incineration has the advantage of greatly reducing the volume of radioactive material that must be stored. However, temperatures of about 1500.degree. F. are required to completely oxidize the organic materials in the filters, and at these temperatures heavy metals such as lead and arsenic, and radionuclides, such as ruthenium, may be volatized and present an environmental hazard. In addition, the filters contain significant amounts of radium which remains in the ash and requires extensive precautions to remove and dispose of.
Another method of disposing of the cartridges is to chop them up and encapsulate them in cement. While this is a widely accepted method of disposal, it greatly increases the volume of waste material that must be stored.
Still another possibility for disposing of the filter cartridges is to dissolve them in an organic solvent and chemically treat the solution. However, these cartridges consist of acrylic fiber and wood pulp bonded with a phenolic resin, and crosslinked phenolic resins are impervious to most types of chemical attack. Powerful solvents such as N-methyl-pyrrolidone, tetrahydrofuran, dioxane, and trichloroethylene all fail to disintegrate or dissolve the filters. Even caustic soda and dimethyl formamide, which were recommended by the seller of the filters, are ineffective in degrading or dissolving the filter cartridges.